1. Field of the Invention
This invention concerns contactless transceiver devices designed to ensure the traceability of objects and particularly concerns a contactless label with an omnidirectional antenna.
2. Description of Related Art
At present, contactless transceiver devices are widely used in numerous applications. One of these applications is the contactless smart card, which is being increasingly used in various sectors, such as the public transport sector, for example. They have also been developed as a means of payment. The exchange of information between a contactless device and the associated reader is accomplished by remote transmission of electromagnetic signals between an antenna housed in the contactless device and a second antenna located in the reader. For developing, storing and processing the information, the device is equipped with a microcircuit connected to the antenna and including a memory zone. During the exchange of information, the contactless device is powered by electromagnetic waves transmitted by the reader.
Another application of contactless devices that is becoming more and more important is their use as labels affixed on objects for identification purpose when performing tracking of goods or inventory position. In these applications, the microcircuit of the label affixed on each object contains in memory the data of the object, which allows the object to be indexed and identified and thereby ensures its traceability.
The label is affixed on the object at the time of its manufacture and remains on it until it is received by the client. The memory of the microcircuit contains information about the characteristics of the object or its contents, if it is a container. This information can be read at all times by a reader. Currently, the frequencies commonly used by the reader for the exchange of data with the label are ultra high frequencies (UHF) of around 900 MHz, which allow the label to be read from a distance of more than 2 meters.
A simple antenna that may be used in contactless labels is the dipole antenna shown in FIG. 1 whose dimension is approximately half a wavelength for the frequency used. The special feature of such a dipole resides in the fact that the energy is radiated mainly in a preferential direction perpendicular to the axis of the dipole as shown in the pattern of FIG. 2. As a result, a simple dipole used as an antenna has the major drawback of emitting directional radiation.